Dynamic balance indicating system



June 19, 1951 c, [NGRAHAM 2,557,659

DYNAMIC BALANCE INDICATING SYSTEM Filed Nov. 13. 1945 FIG. 1 FIG. 2

INVENTOR ELMER CLARK INGRAHAM ATTORNEY Patented June 19, 1951 Elmer; Clarle. Ingraham, Cambridge,- Mass.; as-.--- signon by,- mesne. assignments,. to. the- United SIatesof-TAineriGa as re .retary of the Navy;

presentedfb'y,theistic- ApplicationzNovemberrm, 1945;.=SerialNo.-628;285

2 Claims. 1r

This invention relates to methods. and appae ratus for'the' dynamic balancing offirotors.and. more particularly, to methods and apparatus for pensivea-and complicated deyicesifor determiningm.

this soffset or; out-ofrbalanceihave. been used; but these ede-vicescwere ,frequently, unsatisfactorysbecause: of their complicationsandialong :tedious processes necessary to determine the out-of-balance of a rotor.

It is an object of my invention to provide a centrifugal balance indicator to determine the out-of-balance of a rotor.

It is a further object of my invention to provide a simple and inexpensive centrifugal balance indicator.

Other objects and advantages of this invention will be apparent from the following description and drawings in which:

Fig. 1 is a side View of an embodiment of my invention;

Fig. 2 is a front view of the same embodiment; and

Fig. 3 illustrates a method using my invention whereby the out-of-balance and the relationship of the true axis to the mechanical axis of a rotor may be obtained.

In Fig. 1 is disclosed a centrifugal balance indicator which comprises a ball l free to roll in an annular ball race I I, a retaining flange [2 around ball race I l as shown, a hub 13 with recessed adjusting screws M in it, and a web l5 connecting hub l3 to ball race I I. All cylindrical surfaces are concentric and the radial surfaces are perpendicular to the axis of hub l 3.

In Fig. 2 are shown graduated index marks IS on the face of retaining flange l2 and race I I.

Referring to Fig. 3 a method of dynamically balancing a rotor I! by means of my invention is disclosed. The rotor I! is floated" in its own bearings l8 and I9, as by rubber suspension. Attached to rotor l1 near each end are two centrifugal balance indicators 2| and 22. The rotor is rotated by a motor 23 through a mechanical linkage represented by dotted line 26. Arranged to project light on centrifugal balance indicators 2| and 22 are two variable frequency stroboscopic lights 24 and 25, whose frequency is adjusted to that of the rotor.

Ball l0 may be considered as a continuously 2 .11 variably. positioned test weightrwhose.motiornis... restrictedby ace I l and retaining, flange. l2 so that .itspath is... concentric with the-.rotorrto be:v balanced.. Adjustingscrews ,HL are.used.-to-..a tach andadjust hub -.l 3, and .thusrace I I, soethat... it is concentric with the rotor to be balancede To..ba1ance a. rotor using. my. invention, the

rotor isfirst flOated? in. its own bearingsso that. it canbe. rotated 1 on its mechanical..axis.,but is..

freerto. find and ;rotatev on its. .own two axis... A.

centrifugal balanceindicator ismounted-omand; is adjusted so that it is .concentricwith. each; end. of.,the;rotor shaft.v Under synchronized.strobo.-.. scopic .light.-the. motionaisestoppedtand ,the...posis tion of the ball relative to its race can be seen. If the rotor is unbalanced when rotated at a sulficient speed to cause it to seek and rotate on its own true axis, due to centrifugal force acting on it, the ball will come to rest relative to its race. If the rotor is balanced when rotated, the ball will not come to rest in its race but will continue to move.

When the rotor is rotated in its own bearing at a speed-suflicient to cause it to seek and rotate on its own true axis, each end of the rotors mechanical axis and therefore each indicator assumes the motion of a simple eccentric cam, provided that the rotor is unbalanced and its true axis does not coincide with its mechanical axis. This speed is higher than what is usually referred to as the critical speed. The critical speed of a rotor may be defined as that speed just suflicient to cause the rotor to seek and rotate about its true axis instead of about its apparent geometric axis. Due to centrifugal force acting on it, the ball in each indicator seeks and comes to rest relative to its race and therefore to the rotor, at a point which is farthest from the true axis of the rotor. By observation under stroboscopic light the positions of these points relative to the index marks on the retaining flange and thus to the rotor may be easily obtained. In each indicator the ball will assume a position on that side of the indicator corresponding to the lighter side of the body so as to act in itself as a weight tending to balance the rotating system. These points determine diameters at either end through which both the true and mechanical axis pass. From the knowledge of therelative location of the two axes, suitable points for weight adjustments are obtained. Trial weights are then attached at these points and a second determination is made. An extrapolation of these two tests with knowledge of the eccentricity of the above-mentioned motion will very accurately reveal the additional weight shifting required to obtain dynamic balance.

The invention is to be limited only by the appended claims.

What is claimed is:

1. A centrifugal balance indicating system for a rotor comprising an indicator, said indicator comprising, a ball, a ball race, a retaining flange on and concentric with said race, a. hub concentrio with said race, adjusting screws in said hub to attach and to position said hub so that it is concentric with said rotor, and a web connecting said hub to said race, said retaining flange being graduated with index works, said ball being free to rotate in said race with minimum friction, whereby as said rotor, with said hub attached and properly positioned is rotated in its own bearings at a speed sufficient to cause said rotor to seek and rotate on its own true axis, said ball, due to centrifugal force acting thereon, seeks and comes to rest, with said rotor unbalanced, relative to said race at that point farthest from said true axis of said rotor and means for intermittently illuminating said indicator at a frequency synchronous with the frequency of rotation of said rotor.

2. A dynamic balance indicating system for a rotor comprising in combination means for mounting said rotor whereby said rotor is rotatable about its own mechanical axis and is adapt- 30 ed to seek and rotate about its own true axis, said mounting means comprising bearings for each end of th shaft of said rotor mounted in resilient material, a first and second indicator mounted on said shaft concentrically of said rotor and on either side of said rotor, each of said indicators comprising a ball race, a ball, said ball being free to rotate in said race, a hub concentric with said race, adjusting screws on said hub on both sides of said ball race for attaching and positioning said hub concentrically of said rotor, a web connecting said hub to said race, a retaining flange secured to said race, said retaining flange being graduated with index marks, means for rotating said rotor, and illuminating means for periodically illuminating said indicators, the frequency of said periodic illumination being adjusted to be synchronous to the frequency of rotation of said rotor, said illuminating means being adapted to simultaneously illuminate said ball and said flange of each of said indicators.

ELMER CLARK INGRAHAM.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,876,524 Thearle Sept, 6, 1932 1,949,603 Davey Mar. 6, 1934 FOREIGN PATENTS Number Country Date 400,880 Great Britain Nov. 2, 1933 419,282 Great Britain Nov. 8, 1934 532,828 Germany Sept. 8, 1931 

